Field of the Invention
The present invention relates to a method of manufacturing an annular material represented by a turbine disk of an engine for an aircraft. Particularly, the present invention relates to a manufacturing method related to an annular material having excellent uniformity.
Background Art
Hitherto, an annular material made of an alloy such as a Ni-based alloy, a Fe-based alloy, or a Co-based alloy is known. For example, an annular material made of a Ni-based alloy having excellent high-temperature strength is used in a turbine disk of an engine for an aircraft, and the turbine disk as a product is manufactured by machining the annular material.
A plurality of turbine blades is arranged in the outer circumference portion of the turbine disk along the circumferential direction. In the engine for an aircraft, as high-temperature and high-pressure combustion gas generated in the engine flows from the front side to the rear side in the axial direction thereof in the outer circumference portion of the turbine disk, the turbine blades are rotated at high speed along with the turbine disk. The driving force of the rotation is transmitted to a compressor and fans arranged on the front side of the turbine disk, thereby obtaining compressed air and propulsion needed for continuous combustion.
The turbine disk is positioned in an important rotating part, and the annular material used in the turbine disk requires sufficient mechanical strength. Specifically, in the turbine disk, the outer circumference portion thereof is exposed to the combustion gas and is thus at a high temperature of about 600 to 700° C., while the temperature of the inner circumference portion is suppressed to be relatively low. As a result, as the engine starts up and stops, thermal stress repeatedly occurs therein. Therefore, the turbine disk requires excellent low-cycle fatigue property and needs to also have high creep strength property because the outer circumference portion thereof receives centrifugal force caused by high-speed rotation about the shaft at high temperature. In addition, the turbine disk also requires high tensile and yield strength.
In order to ensure mechanical strength capable of responding to such various demands, the annular material used in the turbine disk is generally manufactured by forging (forging press) (for example, refer to Japanese Patent Application, First Publication No. H07-138719 and Japanese Patent Application, First Publication No. S62-211333). That is, by applying strain to the annular material through forging and increasing the fineness of the grains thereof, tensile strength, fatigue strength, and the like are enhanced. As a facility applied to forging, a hydraulic control forging press which enables strict control of forging speed is desired. In order to obtain the uniformity in the circumferential direction of the structure (grains) in the annular material, it is recognized that application of entire surface forging in which the entire element is made at the same time is preferable.
In recent years, due to demand for an increase in the output of the engine for an aircraft, an increase in the size of the turbine disk is required. In a case of increasing the size of the annular material due to the increase in the size of the turbine disk, a large-sized hydraulic control forging press of several tens of kilotons class, is needed (for example, refer to “an investigation and research report on the development of an innovative member using a supersized press machine for forging as an investigation report in 2002”, by New Energy and Industrial Technology Development Organization, March, 2003, p. 10, 11, and 37 to 41).
However, the large-sized hydraulic control forging press described above is very expensive and rare in the world. Therefore, in a case of using such a large-sized hydraulic control forging press, a supply capability of the annular material is limited, and the product cost is maintained at a high level. In addition, the tendency to increase the size of the turbine disk in recent years becomes to a degree at which closed die forging is difficult although the large-sized hydraulic control forging press is used, and thus it is difficult to obtain desirable mechanical property in a partial region of the annular material subjected to the forging and it is difficult to ensure uniformity of the structure thereof.
On the other hand, instead of manufacturing the annular material using a forging press, a making method through ring rolling is considered. In this case, facility costs may be reduced, and it is easy to cope with the increase in the size of the annular material. However, in general, ring-rolled product is more likely than a press-forged product to have anisotropy of mechanical property (strength property) and this is not appropriate for a product that requires isotropy of mechanical property as in the turbine disk.
In addition, a method of making an annular material by combining forging press and ring rolling is also considered. However, in order to obtain a desired uniform and fine structure, there is a need to further perform final forging after the ring rolling, and thus the manufacturing process becomes complex and the manufacturing costs are increased.